Multiple POP/SMTP Accounts Bug - Mail uses wrong 'from' address

Question

I've be scratching my head over this but can't see anything else wrong so I figure it must be a bug with Mail 4.2:
I have multiple POP3/SMTP accounts configured, lets say:
[email protected], to receive on pop.blah1.com and send on smtp.blah1.com
[email protected], to receive on pop.blah2.com and send on smtp.blah2.com
If I create emails sourced from [email protected], they are sent just fine.
However if I try to email from [email protected], I get a pop-up telling me that smtp.blah2.com is offline and I need to select another SMTP server.
I checked the server settings a hundred times over and also resorted to telnetting to port 25 of blah2.com to ensure it was full working (yes it was!).
[Even Connection Doctor thinks the servers are all good]
So next I try telling emails sourced from [email protected] to send via smtp.blah1.com - Eureka, it works!
But this is a little odd - so I check the received email headers and compare these with the 'Sent' header.
It appears that mail thinks its sending the email from [email protected] but the email actually ends up being sourced from [email protected]!
So I can only presume that Mail is marking the smtp.blah2.com server as down because it is trying to use the wrong source address when sending a message and therefore being refused by the SMTP relay.
Has anyone else seen this?

Answer 1

Thanks chaps,
The other accounts are direct POP3/SMTP to my hosted servers - they are not passing through GMail and so it couldn't cause the issue.
I have, however, found the problem inadvertently while trying to run a comparison with Thunderbird - the good news is, its not Mail as such, though it does raise a couple of other questions...
Basically, whichever SMTP server is running on my hosted servers, it does not allow a message with no text in the body, while Google's SMTP implementation clearly does.
As my test messages only had a subject line, they were failing on my servers but working OK with GMail.
The questions therefore are:
1. Shouldn't Mail pad an empty message to ensure it goes (MS Outlook works fine with empty messages but interestingly Thunderbird also doesn't)
2. Even assuming its OK to use GMail's SMTP as a relay, shouldn't Mail use the correct source address rather than making it look like the emails came from my GMail account?
- I'm not sure if this is 'allowed' with modern SMTP from a security perspective but I think that some services support it.
Thanks for all your input!
J